A. Field of the Invention
The present invention relates to a friction engagement portion of a clutch disk assembly having friction pads made of sintered alloy.
B. Description of the Related Art
In general, it is desirable for a clutch disk assembly to have a generally large torque transmitting capacity. A facing of a friction engagement portion of the clutch disk is generally made of glass fiber, resin, rubber or the like. However, the facing made of such a material may not have a sufficiently large torque transmitting capacity.
In order to ensure a large torque capacity, some clutch disks use sintered bodies (which will be referred to as "sintered alloy pads") made of a mixture of ceramic powder and metal powder. These clutch disks are generally produced by heating (under pressure in some cases) ceramic powder and metal powder disposed on a copper-plated core plate of iron.
In the clutch disk assembly having such a conventional sintered alloy pad, the clutch disk (friction member) does not have a cushioning effect, and thus causes a large shock or jolt in an automobile as the clutch is being engaged.
In view of the above, in such a clutch disk structure, there may be employed that a pair of plate members that include corrugated portions which form convex surfaces. Spaces are defined between the plate members due to the convex surfaces. Separate sintered alloy pads are fixed to each of the plate members by rivets, one set of rivets extending through one plate member and another set of rivets extending through the other plate member. Consequently, the rivets extend through surfaces of each plate member adjacent to one another. According to this structure, the convex surfaces of the plate members bend to exhibit a cushioning effect in the clutch engaging operation.
However, the adjacent surfaces of the paired plate members having rivets extending therethrough are such that the degree of cushioning effect is restricted by contact between the heads of the rivets and the adjacent surface of the adjacent plate member. Even if positions of the rivet heads are spaced apart to avoid mutual contact or interference, the rivet heads are unavoidably brought into contact with the adjacent surface of the plate members, so that the degree of cushioning effect is restricted. Since only the rivet heads are brought into contact with the adjacent surface of one of the plate member in the cushioning operation, contact pressure is localized and is not uniformly on the sintered alloy pads, so that local wearing occurs in the area where the rivet heads make contact.
Clutch disk assemblies used in a passenger car may also include friction engagement portions which are made of an organic material such as glass fiber, resin, rubber or the like, in addition to the type described above having sintered materials. In the clutch disk using organic friction members, a cushioning plate is disposed between paired friction facings opposed to each other, so that the cushioning plate reduces a shock in the clutch engaging operation.
A problem with the conventional clutch disk assembly having a cushioning plate is that the cushioning characteristics of the assembly have a generally linear form. It is difficult to achieve intended cushioning characteristics in spite of the provision of the cushioning plates. For example, if the cushioning characteristics are set principally for suppressing shudder, then noises cannot be adequately prevented. Alternatively, if the cushioning characteristics are set principally for suppressing noises, shudder cannot be adequately suppressed.
In particularly, it desirable to overcome these problems in the clutch disk using the sintered alloy pads, because the clutch disk using sintered alloy pads produces both shudder and unwanted noises during usage.